Magnetic encoders using a rubber magnet are excellent for detection of revolution rate at a low speed and recently have been widely used in wheel speed sensors, etc. Wheel speed sensors are used in the neighborhood position of wheel, requiring good water resistance and a saline water resistance. The magnetic encoder using a rubber magnet comprises a stainless steel sheet, a rubber magnet, and an adhesive for bonding these two. Water resistance tests show that peeling occurred at the interface between the stainless steel sheet and the adhesive of the magnetic encoder, and the water resistance of the adhesive as well as the rubber magnet itself is regarded as very important.
For the adhesive layer for the water resistance purpose, epoxy resin is usually used, but owing to poor adhesion to the stainless steel sheet, the epoxy resin is not used alone in case of the stainless steel sheet. In case of a single adhesive layer, a phenol resin-based adhesive, a silane-based adhesive, an epoxy resin/silane-based adhesive, or the like is used. In case of two adhesive layers, the afore-mentioned phenol resin-based adhesive, a phenol resin/halogenated polymer-bases adhesive, a phenol resin/epoxy resin-based adhesive, or the like is used as an under coat. However, even if these under coat adhesives are used in combination with various top coat adhesives, no statisfactory water resistance can be obtained in severe circumstances such as saline water spraying.